Connection for a coiled lead to an electrical contact for an implantable medical device

ABSTRACT

High reliability electrical connections between a helical strand and flat electrodes, such as strip electrodes found in implantable neurostimulator system, are described. The connection consists of a crimp joint in which an inside diameter mandrel is used to provide the coil with sufficient radial rigidity to ensure structural integrity of the crimp. The mandrel is made of a relatively soft biocompatible material that deforms rather than damages the fine wires of the helical strand during crimping. The crimp is accomplished by radial deformation of an annular or semi-annular crimping member that receives the helical strand/mandrel assembly.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No.10/968,310, filed Oct. 19, 2004, now U.S. Pat. No. 7,383,090, whichclaims priority from provisional application Ser. No. 60/512,739, filedOct. 20, 2003.

BACKGROUND OF THE INVENTION

This invention relates to high reliability electrical attachmentsbetween coiled leads and flat electrodes, such as strip electrodes foundin implantable neurostimulator systems. The requirements for theattachment are biocompatibility, isolation from body fluids, andlong-term mechanical/electrical continuity under cyclic stress.

A typical strip electrode consists of a thin, flat electrical contact ofbiocompatible, conductive material. A typical lead consists of a tightlywound coil of one or more helical strands of fine, fatigue resistantwire or filar elements. After attachment of the helical strand to theelectrical contact, the entire assembly is potted or embedded in a flatsheet of elastomer so that only the face of the contact is exposed tobody fluids.

Implantable leads are made of wires typically about 0.002 inches to0.004 inches in diameter. These wires are formed into coils or helicalstrands about 0.015-inches in diameter. Leads are coiled so they canwithstand constant flexing and bending forces as a result of bodymovement. Because of the very fine wire diameters, however, theresulting helical strands are difficult to attach to electrical contactsby laser welding. Crimping is the preferred attachment method. In thatrespect, the present invention is directed to ensuring that the crimpedconnection between a helical strand and an electrical contact maintainsthe same degree of reliability as is built into the coiled lead itself.

SUMMARY OF THE INVENTION

The connection between a coiled lead or helical strand and an electricalcontact consists of a crimp joint in which an inside diameter mandrel isused to provide the coil with sufficient radial rigidity to ensurestructural integrity of the crimp. The mandrel is made of a relativelysoft biocompatible material that deforms rather than damages the finewires of the helical strand during crimping. The crimp is accomplishedby radial deformation of an annular or semi-annular crimping member thatreceives the helical strand/mandrel assembly.

In one embodiment, the crimping member is a porous, deformable diskhaving an axial hole that receives the electrical contact and a radialhole that receives the helical strand/mandrel assembly. This deformablecrimping member is subjected to a cold coining process that provides asecure crimp joint to the helical strand/mandrel assembly with a portionof the crimping member being extruded into a circumferential groove orchannel in the central electrical contact. In that manner, the deformedcrimping member creates a secure connection to the helical strandcomprising the lead as well as to the electrical contact.

In another embodiment, there is no deformable crimping member. Instead,the electrical contact made of a porous sintered material is itselfdeformable. That way, the electrical contact is provided with a radialbore that receives the mandrel supported in the lumen at the distal endof the helical strand. This assembly is inserted into the radial bore inthe contact, which is then deformed into a locking relationship with thehelical strand and mandrel.

In another embodiment, as before, the integrity of the crimp is enabledby the presence of a relatively soft mandrel positioned inside thediameter of the helical strand. The mandrel has a distal portion that issecured to the back of the electrical contact by means of a weld, braze,or solder joint. Alternatively, the distal portion of the mandrel isinserted into a through-hole in the electrical contact, secured from thetop face, and then bent over until the helical strand/mandrel connectionis parallel to the back face of the contact. In any event, the crimpingmember consists of an annular or semi-annular crimp socket surroundingthe helical strand/mandrel assembly.

These and other aspects of the present invention will become moreapparent to those skilled in the art by reference to the followingdescription and to the appended drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view, partly in phantom, showing an implantablemedical device 10 connected to a pair of strip electrodes 20 and 22 byrespective coiled leads 16 and 18.

FIG. 2 is a cross-sectional view along line 2-2 of FIG. 1.

FIG. 3 is a side elevational view, partly in cross-section, showing ahelical strand 16D of the coiled lead 16 crimped to an electricalcontact 30 according to the present invention and encased in anelastomeric material 32.

FIG. 4 is a side elevational view, partly in cross-section, showing theelectrical contact 30 prior to being moved into the central opening 56in a deformable crimping member 46 and the helical strand 16D/mandrel 44prior to being moved into an axial bore 58 in the crimping member.

FIG. 5 is a side elevational view, partly in cross-section, of theelectrical contact 30 seated in the deformable crimping member 46.

FIG. 6 is a side elevational view, partly in cross-section, of thehelical strand 16D/mandrel 44 seated in the deformable crimping member46.

FIG. 7 is a side elevational view, partly in cross-section, showing anannular punching ram 72 prior to deformation of the crimping member 46.

FIG. 8 is a side elevational view, partly in cross-section, showing thecrimping member 46 being deformed by the punching ram 72.

FIG. 9 is a side elevational view, partly in cross-section, of anotherembodiment of a helical strand 114/mandrel 112 assembly prior to beingmoved into the axial bore 110 of a deformable electrical contact 102.

FIG. 10 is a side elevational view, partly in cross-section, showing thehelical strand 114/mandrel 112 of FIG. 11 moved into the bore 110 in thedeformable electrical contact 102.

FIG. 11 is a side elevational view, partly in cross-section, showing apunching ram 116 beginning to deform the electrical contact 102.

FIG. 12 is a side elevational view, partly in cross-section, showing thehelical strand 114 crimped to the electrical contact 102 and encased inan elastomeric material 116.

FIG. 13 illustrates another embodiment of an electrical contact 102Ahaving its upper surface 106A spaced above the elastomeric material 116.

FIG. 14 is a side elevational view, partly in cross-section, showing aconnection for a helical strand 124 to the electrical contact 102according to the prior art.

FIG. 15 is a side elevational view, partly in cross-section, showing thepresent invention connection of the helical strand 114 to the electricalcontact 102.

FIG. 16 is a side elevational view, partly in cross-section, of anotherembodiment of a headed mandrel 136 crimped to a helical strand 134secured to an electrical contact 132 and encased in an elastomericmaterial 148.

FIG. 17 is a side elevational view, partly in cross-section, of anotherembodiment of a mandrel 156 supported by a helical strand 154 secured toan electrical contact 152 and encased in a elastomeric material 166.

FIG. 18 is a side elevational view, partly in cross-section, of anotherembodiment of a mandrel 178 crimped to a helical strand 174 secured tothe land 190 of an electrical contact 172 and encased in an elastomericmaterial 194.

FIG. 19 is a side elevational view, partly in cross-section, of anotherembodiment of a mandrel 208 crimped to a helical strand 204 secured toan electrical contact 202 provided with a flange 216 and encased in anelastomeric material 220.

FIG. 20 is a side elevational view, partly in cross-section, of anotherembodiment of a mandrel 238 crimped to a helical strand 234 secured to adeep drawn electrical contact 232 and encased in an elastomeric material252.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings, FIG. 1 illustrates an implantable medicaldevice 10 comprising a housing 12 supporting a header 14 connectingcoiled leads 16 and 18 to respective strip electrodes 20 and 22. Thehousing 12 is of a conductive material, such as of titanium or stainlesssteel. Preferably, the medical device housing 12 comprises matingclamshell portions 24 and 26 in an overlapping relationship. Theclamshell housing portions are hermetically sealed together, such as bylaser or resistance welding, to provide an enclosure for controlcircuitry (not shown) connected to a power supply (not shown), such as abattery. There may also be a capacitor for a medical device such as adefibrillator. U.S. Pat. No. 6,613,474 to Frustaci et al. contains amore detailed description of a housing comprising mating clamshellportions. This patent is assigned to the assignee of the presentinvention and incorporated herein by reference. The housing 12 can alsobe of a deep drawn, prismatic and cylindrical design, as is well knownto those skilled in the art.

The header 14 is mounted on the housing 12 and comprises a body ofmolded elastomeric material supporting terminal blocks (not shown) thatprovide for plugging the proximal ends of leads 16 and 18 therein toelectrically connect them to the control circuitry and power supplycontained inside the housing. The distal ends of the leads 16, 18connect to the respective strip electrodes 20 and 22. For a moredetailed description of the header assembly, reference is made to U.S.Pat. No. 7,167,749 to Biggs et al., which is assigned to the assignee ofthe present invention and incorporated herein by reference.

The strip electrodes are surgically secured to body tissue whose properfunctioning is assisted by the medical device. In that respect, theimplantable medical device 10 is exemplary of any one of a number ofknown implantable therapeutic devices such as spinal cord stimulationdevices, vagus nerve stimulation devices for epilepsy, and functionalelectrical stimulation devices for paralysis, and the like. For example,in an implantable pulse generator for spinal cord stimulation to controlpain, the circuitry provides a pulsed stimulating signal that can becurrent controlled or voltage controlled. The signal is delivered tonerves entering the spinal cord by means of implanted insulated coiledleads terminating at strip electrodes such as those shown in FIG. 1.

The strip electrodes 20 and 22 can be similar or different inconstruction. Strip electrode 20 comprises four electrical contacts 24,26, 28 and 30, each having a circular shape in plan view and potted inan elastomeric material 32. Strip electrode 22 comprises four electricalcontacts 34, 36, 38 and 40 potted in an elastomeric material 42. Thesecontacts are square, triangular, hexagonal, and rectangular in planview, respectively. In that respect, the present invention is notlimited to the exact shape of the electrical contact and is adaptable tocontacts having a myriad of shapes in plan form. Nonetheless, thepresent invention will be described with respect to strip electrode 20shown in greater detail in FIG. 2 with the understanding that stripelectrode 22 is generally similar in construction.

As shown, each electrical contact 24, 26, 28 and 30 is individuallyconnected to the medical device 10 by a helical strand or filar of thecoiled lead 16. Suitable materials for the electrical contacts includecarbon such as pyrolytic carbon, titanium, zirconium, niobium,molybdenum, palladium, hafnium, tantalum, tungsten, iridium, platinum,gold, and alloys thereof. Stainless steel, MP35N®, ELGILOY® are othersuitable alloys. The helical strands can be co-axial or they can becoiled side-by-side along the length of the coiled lead 16 until itenters the elastomeric material 42 of the strip electrode 20. There, theindividual helical strands 16A, 16B, 16C and 16D separate from thebundle and connect to the individual electrical contacts 24, 26, 28 and30, respectively. Each helical strand is formed of a conductive, fatigueresistant material such as ELGILOY® (cobalt 40%, chromium 20%, nickel15%, molybdenum 7%, manganese 2%, carbon <0.10%, beryllium <0.10%, andiron 5.8%, by weight) or MP35N® (nickel 35%, cobalt 35%, chromium 20%,and molybdenum 10%, by weight) alloys. The coiled leads comprised of thehelical strands exhibit the desired mechanical properties of lowelectrical resistance, high corrosion resistance, flexibility, strengthand fatigue resistance required for long term duty inside a human body,and the like.

FIG. 3 shows a cross-sectional, view of helical strand 16D secured toelectrical contact 30. A deformable mandrel 44 is inserted into thedistal end of the helical strand 16D. Suitable materials for the mandrelinclude stainless steel, titanium, zirconium, niobium, molybdenum,palladium, hafnium, tantalum, tungsten, iridium, platinum, gold, andalloys thereof. A crimping member 46 is then coined into locking contactwith the helical strand 16D and the surrounded electrical contact 30.The process for coining the helical strand 16D into this lockingrelationship will now be described in greater detail in the progressionof FIGS. 4 to 8.

As shown in FIG. 4, the deformable crimping member 46 in the form of aporous sintered disc has an annular outer sidewall 48 and an annularinner sidewall 50, both extending to an upper surface 52 and a lowersurface 54. A circular, axial opening 56 is formed in the disc by theinner annular sidewall 50. A radial bore 58 extends from the outerannular sidewall 48 to the inner annular sidewall 50 and the circularopening 56. The radial bore 58 is located approximately an equaldistance from the upper and lower surfaces 52, 54 and is sized toreceive the electrical contact 30. The electrical contact 30 has acircular cross-section, comprising an annular sidewall 60 extending toan upper face 62 and a lower face 64. An annular groove or channel 66recessed in the sidewall 60 surrounds the electrical contact and isspaced closer to the lower face 64 than the upper face 62.

As shown in FIGS. 4 and 5, the electrical contact 30 is received in thecircular opening 56 in the deformable crimping member 46 such that thedisc sidewall 60 is in a tight-fitting relationship with the innerannular sidewall 50 thereof.

As shown in FIGS. 4 to 6, the helical strand 16D provides a lumen 68receiving the tapered mandrel 44 at its distal end. The mandrel 44 has acylindrically shaped sidewall received in the helical strand lumen in atight-fitting relationship. Preferably, the mandrel diameter is slightlylarger than the inside diameter of the helical strand so it stays inplace inside the coil while it is being assembled. A planar distal end70 of the mandrel 44 is recessed somewhat inside the distal end of thestrand 16D. The reason for this is to have the helical strand/mandrelcontact interface as great as possible. A proximal end thereof taperstoward the longitudinal axis of the mandrel 44. The taper has a radiusedprofile with the radius being about 10 to about 20 times the diameter ofthe mandrel. The helical strand 16D and mandrel 44 received in the lumen68 thereof is then received in the axial bore 58 of the deformablecrimping member 46 with the planar distal mandrel end 70 spaced from theinner disc annular sidewall 50 defining the opening 56. In thisposition, the longitudinal axis of the mandrel is spaced somewhat towardthe upper surface 52 of the deformable crimping member 46 with respectto the center of the annular groove 66.

As shown in FIG. 7, this assembly is loaded in an open-die punchingfixture having an annular ram 72 sized to the exact shape of the uppersurface 52 of the deformable crimping member 46 surrounding theelectrical contact 30. The porous crimping member is formed bylow-pressure pressing or by loose bed sintering of powdered stainlesssteel, titanium, platinum, or platinum alloy. The powder may be atomizedspherical powder particles, or, preferably, “sponge” powder (such aspowders reduced from a metal chloride), which have higher strength atthe relatively low densities used in the present crimping member. Asintering profile is typically 1,150° C. for three hours at temperaturein vacuum for titanium and stainless steel, or 1,625° C. for three hoursat temperature in air for platinum to produce a low-density structurecombined with a high degree of sintering. The sintered particles haverelatively large diameter interparticle necks, but at a relative densityof only about 60% to 70%. This allows the porous crimping member toundergo cold coining to a density of around 80% during the crimpingprocess while maintaining its structural integrity.

In that respect, a sufficient amount of force is exerted on the crimpingmember 46 to compress it into a final shape having its upper surface 52spaced a relatively short distance from the groove 66. As this occurs,material 46A comprising the crimping member 46 flows by plasticdeformation into the groove 66 to lock the deformable disc to theelectrical contact 30. This deformation also causes the crimping member46 to lock onto the rugosity of the helical strand 16D/mandrel 44assembly. A typical cold coining pressure is about 10,000 psi, which issufficient to increase the density of the deformable crimping member 46,form the crimp, and intrude the inside diameter material of the crimpingmember into the electrical contact without pinching off the fine wiresof the helical strand 16D.

As shown in the final assembly of FIG. 3, encasing the deformablecrimping member 46, helical strand 16 and electrical contact 30 in thebiocompatible elastomeric material 32, such as silicone or polyurethane,completes the strip electrode. After cold coining, a longitudinal axisof the mandrel 44 is substantially centered with the trough of thegroove 66. After cold coining, the annular outer sidewall of thecrimping member assumes the shape of a bulge 48A, which helps lock thepolymer material 32 to the crimping member 46. Before deformation,electrical contact 30 is shown having a circular cross section. However,it may also have a frusto-conical shape before deformation to furtherimprove the interlock with the elastomeric material.

Only the upper face of the electrical contact 30 is left exposed. Thissurface may be impregnated with liquid silicone or other biocompatibleresin that is then polymerized to seal the porosity, and to keep bodyfluids from infusing into the porous electrode and reaching the coiledlead. The remaining surfaces of the electrical contact 30 exposed to theelastomeric material is preferably roughened by grit blasting, machiningmarks, knurling, and the like to improve adhesion of the pottingmaterial to the electrode and stabilize the electrode position.

FIGS. 9 to 12 illustrate another embodiment of a strip electrode 100according to the present invention. The electrode comprises a poroussintered deformable electrical contact 102 having a surrounding sidewall104 extending to upper and lower surfaces 106 and 108. Suitablematerials for the contact 102 include titanium, zirconium, niobium,molybdenum, palladium, hafnium, tantalum, tungsten, iridium, platinum,gold, and alloys thereof. An annular bore 110 enters the body from thesidewall 104, spaced closer to the lower surface 108 than the uppersurface 106.

As shown in FIG. 10, a tapered mandrel 112, similar to the previouslydescribed mandrel 44, supported in the lumen at the distal end of ahelical strand 114 are received in the bore 110. A pressing ram 116 thendeforms the electrical contact 102 into locking contact with therugosity provided by the coils of the helical strand 114. The electricalcontact 102 has a relative density of about 60% to about 70% prior tobeing deformed under the compression pressure and about 80% after beingdeformed into the locking relationship.

Encasing the deformed electrical contact 102 and helical strand 114 in abiocompatible elastomeric material 116, such as silicone orpolyurethane, completes the electrode 100. After cold coining, thesurrounding sidewall of the electrical contact assumes the shape of abulge 104A. This helps lock the polymer material 116 to the contact.only the upper active surface 106 of the electrical contact 102 is leftexposed. In a similar manner as the contact 30 in FIGS. 1 to 8, thisupper surface 106 may be impregnated with liquid silicone or otherbiocompatible resin that is then polymerized to seal the porosity and tokeep body fluids from infusing into the porous electrode and reachingthe coiled lead.

In FIG. 12, the upper surface 106 of the electrical contact 102 issubstantially coplanar with that of the elastomeric material 116. InFIG. 13, the upper surface 106A of the electrical contact 102A is spacedabove the upper surface of the elastomeric material.

An important aspect of the present embodiments illustrated in FIGS. 1 to12 is that the extended, tapered mandrels 44, 112 distribute thebending, flexing and twisting strain forces caused by body movement overa greater length of the helical strands 16D, 114 than in a mandrelhaving a blunt end. This is shown in FIG. 15 by the gap of arrowsdesignated 118 in comparison to the strain distribution indicated by thegap of arrows 120 afforded by a mandrel 122 having a blunt endconstruction according to the prior art as shown in FIG. 14.

The length of gap 118 is about 1 to 5 diameters of the helical strand,preferably about 2 to 3 diameters. In the blunt end mandrel 122, strainforces on the helical strand 124 moving along a 20° arc aresignificantly more concentrated in comparison to a similar degree ofmovement in the present construction.

Another embodiment of a strip electrode 130 comprising an electricalcontact 132 secured to a helical strand 134 according to the presentinvention is shown in FIG. 16. Machining, stamping, metal injectionmolding, drawing, and any other suitable method can make the contact132. In the case of machining and metal injection molding, themandrel/contact assembly may also be formed as a single integral unit.This electrode comprises a mandrel 136 having a tapered nose 138received in the lumen of the helical strand 134. A significant portionof the mandrel 136 extends out the distal end of the helical strand 134.A distal end of the mandrel 136 is in the shape of a spherical ball 140sized about 0.010 inches larger in diameter than that of the mandrel.The distal ball 140 is secured to the back face 142 of the electricalcontact 132 by braze, weldment, or solder joint 144. An effective brazeload is about 10 mg of gold at a temperature of about 1,100° C. for twoseconds at temperature. Many other braze materials other than gold canbe used, however, for example gold—tin or copper—silver braze alloys.

An annular or semi-annular socket 146 is positioned on the distal end ofthe helical strand 134 with the mandrel received in the lumen thereof.The crimp is accomplished by radial deformation of the socket 146. Thatway, the material of the socket 146 plastically deforms into therugosity of the helical strand 134 that, in turn, tightly surrounds thecylindrical intermediate section of the mandrel 136. Materialsappropriate for the socket 146 include stainless steel, titanium,niobium, zirconium, platinum and platinum alloys, and otherbiocompatible deformable materials. The entire assembly is encased in aelastomeric material 148 such as silicone or polyurethane with only theactive surface 150 of the electrical contact 132 being left exposed.This construction provides improved isolation of the crimp joint frombody fluids that may diffuse along the electrical contact/elastomerinterface.

FIG. 17 illustrates a further embodiment of a strip electrode 150comprising an electrical contact 152 secured to a helical strand 154according to the present invention. A mandrel 156 has its distal endreceived in an axial opening 158 in the contact 152. A braze, weldmentor solder joint 160 secures the mandrel to the contact. Then, themandrel 156 is bent until the longitudinal axis of the helical strand154 is substantially parallel to the upper contact face 162.

Connection of the mandrel 156 to the helical strand 154 is similar tothat shown in FIG. 16 with a deformable socket 164 clamped onto thehelical strand receiving the mandrel. Finally, the entire assembly isencased in an elastomeric material 166, such as silicone orpolyurethane, with only the active contact face 162 left exposed.

FIG. 18 illustrates a further embodiment of a strip electrode 170comprising an electrical contact 172 secured to a helical strand 174 bya deformable crimp socket 176 according to the present invention. Acylindrically shaped mandrel 178 having a tapered nose 180 is receivedin the lumen of the helical strand 174. A distal portion 182 of themandrel 178 extends out the distal end of the helical strand 174. Theelectrical contact 172 comprises a contact face 184 extending downwardlyand outwardly to form a chamfered edge 186. The back face 188 has aprotruding land 190 to which the distal portion 182 of the mandrel issecured by braze, weldment or solder joint 192. To further enhance thisconnection, the distal portion 182 of the mandrel may have a flatsurface received in a coinciding groove or channel in the land 190. Thisassembly is then encased in an elastomeric material 194, such assilicone or polyurethane, with only the contact face 184 left exposed.

FIG. 19 illustrates a further embodiment of a strip electrode 200comprising an electrical contact 202 secured to a helical strand 204 bya deformable crimp socket 206 according to the present invention. Amandrel 208 having a tapered nose 210 is received in the lumen of thehelical strand 204. A distal portion 212 of the mandrel 208 extends outthe distal end of the helical strand 204. The electrical contact 202comprises a contact face 214 extending downwardly to a flange 216. Aswith the strip electrode 170 of FIG. 18, the distal portion 212 of themandrel is cylindrical, flattened or of some other cross-section,received in a coinciding groove or channel on the back face 216 of thecontact 202 secured thereto by a braze, weldment or solder joint 218.This assembly is then encased in a elastomeric material 220 with onlythe contact face 214 left exposed.

FIG. 20 illustrates a further embodiment of a strip electrode 230comprising a deep drawn electrical contact 232 secured to a helicalstrand 234 by a deformable crimp socket 236 according to the presentinvention. A mandrel 238 having a tapered nose 240 is received in thelumen of the helical strand 234. A distal portion 242 of the mandrel 238extends out the helical strand 234. The electrical contact 232 is madeof a conductive metal such as any one previously described as useful forthe contacts shown in alternate embodiments of the present invention.The electrical contact 232 has an upper contact face 244 connected to afrusto-conical portion 246 extending downwardly and outwardly to asurrounding rim 248. The rim 248 is generally parallel to the plane ofthe contact face 244. The distal portion 242 of the mandrel is securedto the rim 248 by braze, weldment or solder joint 250. Preferably, thedistal portion of the mandrel 238 and that portion of the rim 248supporting the mandrel have coinciding shapes for added strength to theconnection. This assembly is then encased in an elastomeric material 252with only the contact face 244 left exposed.

Thus, the present invention has been described with respect to variousstructures and methods for making high reliability electricalattachments between coiled leads and flat electrodes such as stripelectrodes found in implantable neurostimulator systems. The attachmentrequirements of biocompatibility, isolation from body fluids, andlong-term mechanical/electrical continuity under cyclic stress are metby the novel mandrel received in the helical strand connected to theelectrical contact by the deformable crimping member, the deformablecontact itself, or by the mandrel being secured to the contact through abraze, weldment or solder joint.

It is appreciated that various modifications to the inventive conceptsdescribed herein may be apparent to those of ordinary skill in the artwithout departing from the spirit and scope of the present invention asdefined by the appended claims.

1. An electrode for an implantable medical device, the electrodecomprising: a) an electrical contact having an electrical contactsidewall extending from an electrical contact upper face to anelectrical contact lower face, wherein the electrical contact has aradial bore extending from the electrical contact sidewall part wayacross a diameter thereof between its upper and lower faces; b) at leastone electrical conductor extending from a proximal end connectable tothe medical device to a distal portion having a helical shape forming alumen; c) a mandrel comprising a sidewall extending along a longitudinalaxis thereof from a distal mandrel portion to a proximal mandrel portioncomprising a tapered nose that extends downwardly and inwardly along thelongitudinal axis to a proximal end thereof, wherein the mandrel isreceived in the lumen at the distal portion of the at least oneelectrical conductor received in the bore of the electrical contact andwherein the tapered nose of the proximal mandrel portion is received inthe lumen of the at least one electrical conductor, but not in the boreof the electrical contact.
 2. The electrode of claim 1 wherein themandrel has a cylindrical sidewall extending along the longitudinal axisthereof to the tapered nose.
 3. The electrode of claim 1 wherein thedistal mandrel portion received in the distal portion of the at leastone electrical conductor received in the bore of the electrical contactis brazed, welded or soldered thereto.
 4. The electrode of claim 1wherein the electrical contact is a deep drawn member.
 5. The electrodeof claim 1 wherein the tapered nose of the mandrel has a length that isfrom about 1 to 5 times the diameter of the coil of the coiled filar. 6.The electrode of claim 1 wherein the tapered nose of the mandrel has aradiused profile with the radius being about 10 to about 20 times thediameter of the mandrel.
 7. The electrode of claim 1 wherein the upperface of the electrical contact is planar.
 8. The electrode of claim 1wherein an elastomeric material encases at least the distal portion ofthe at least one electrical conductor and at least the sidewall of theelectrical contact, but with the upper face thereof remaining exposed.9. An electrode for an implantable medical device, the electrodecomprising: a) an electrical contact having a sidewall extending to anupper face and a lower face, wherein a radial bore is provided in theelectrical contact sidewall part way across a diameter thereof; b) atleast one electrical conductor comprising a proximal end connectable tothe medical device and a distal portion comprising at least one coiledfilar providing a rugosity; c) a mandrel comprising a cylindricalsidewall extending along a longitudinal axis thereof from a distalmandrel portion to a proximal mandrel portion comprising a tapered noseextending downwardly and inwardly along the longitudinal axis to aproximal end thereof, wherein the mandrel is received in a lumen at thedistal portion of the coiled filar and wherein at least a portion of thecoiled filar supporting the distal mandrel portion is movable into thebore of the electrical contact which is then deformable under acompression pressure to lock onto the rugosity of the coiled filar withthe distal mandrel portion preventing damage to the coiled filar; and d)an elastomeric material encasing at least the distal portion of thecoiled filar and at least a portion of the electrical contact, but withthe upper face thereof remaining exposed.
 10. The electrode of claim 9wherein the elastomeric material encases only a portion of the sidewallof the electrical contact, spaced below the upper face thereof.
 11. Theelectrode of claim 9 wherein the elastomeric material encases the entiresidewall of the electrical contact.
 12. The electrode of claim 9 whereinthe longitudinal axis of the mandrel is spaced closer to the lower facethan the upper face.
 13. The electrode of claim 9 wherein the taperednose of the mandrel has a length that is from about 1 to 5 times thediameter of the coil of the coiled filar.
 14. The electrode of claim 9wherein the tapered nose of the mandrel has a radiused profile with theradius being about 10 to about 20 times the diameter of the mandrel. 15.The electrode of claim 9 wherein the electrical, contact has a relativedensity of about 60% to about 70% prior to being deformed under thecompression pressure and about 80% after being deformed into the lockingrelationship with the coiled filar.
 16. A method for providing anelectrode for an implantable medical device, comprising the steps of: a)providing an electrical contact comprising an electrical contactsidewall extending from an electrical contact upper face to anelectrical contact lower face, wherein the electrical contact has aradial bore extending from the electrical contact sidewall part wayacross a diameter thereof between its upper and lower faces; b)providing at least one electrical conductor extending from a proximalend connectable to the medical device to a distal portion having ahelical shape forming a lumen; c) providing a mandrel comprising asidewall extending along a longitudinal axis from a distal mandrelportion to a proximal mandrel portion comprising a tapered noseextending downwardly and inwardly along the longitudinal axis to aproximal end thereof; d) positioning the mandrel in the lumen at thedistal portion of the at least one electrical conductor; and e)positioning the distal mandrel portion received in the lumen at thedistal portion of the at least one electrical conductor in the bore ofthe electrical contact with the tapered nose at the proximal mandrel endreceived in the lumen of the at least one electrical conductor, but notin the bore of the electrical contact.
 17. The method of claim 16including encasing at least the distal end of the helical strand and atleast a portion of the electrical contact in an elastomeric materialwith the upper face of the electrical contact remaining exposed.
 18. Anelectrode for an implantable medical device, the electrode comprising:a) an electrical contact having an electrical contact sidewall extendingfrom an electrical contact upper face to an electrical contact lowerface, wherein the electrical contact has a radial bore extending fromthe electrical contact sidewall part way into a depth thereof betweenits upper and lower faces; b) at least one electrical conductorextending from a proximal end connectable to the medical device to adistal portion having a helical shape forming a lumen; c) a mandrelcomprising a sidewall extending along a longitudinal axis thereof from adistal mandrel portion to a proximal mandrel portion, wherein themandrel is received in the lumen at the distal portion of the at leastone electrical conductor received in the radial bore of the electricalcontact and wherein the proximal mandrel portion is received in thelumen of the at least one electrical conductor, but not in the bore ofthe electrical contact.
 19. The electrode of claim 18 wherein the radialbore extends from the electrical contact sidewall part way across adiameter of the electrical contact.
 20. An electrode for an implantablemedical device, the electrode comprising: a) an electrical contacthaving a sidewall extending to an upper face and a lower face, wherein aradial bore is provided in the electrical contact sidewall; b) at leastone electrical conductor comprising a proximal end connectable to themedical device and a distal portion comprising at least one coiled filarproviding a rugosity; c) a mandrel comprising a cylindrical sidewallextending along a longitudinal axis thereof from a distal mandrelportion to a proximal mandrel portion, wherein the mandrel is receivedin a lumen at the distal portion of the coiled filar and wherein atleast a portion of the coiled filar supporting the mandrel is movableinto the bore of the electrical contact which is then deformable under acompression pressure to lock onto the rugosity of the coiled filar withthe distal mandrel portion preventing damage to the coiled filar andwith the proximal mandrel portion received in the lumen of the at leastone electrical conductor, but not in the bore of the electrical contact;and d) an elastomeric material encasing at least the distal portion ofthe coiled filar and at least a portion of the electrical contact, butwith the upper face thereof remaining exposed.
 21. The electrode ofclaim 20 wherein the radial bore extends from the electrical contactsidewall part way across a diameter of the electrical contact.